The invention broadly relates to seated body support and is specifically directed to chair devices in which a chair member may be tilted or otherwise moved relative to a chair support.
One of the most difficult problems in chair design is achieving long term comfort, whether task or audience seating is involved. It has been found that maintaining substantially equal pressure distribution throughout the surface area of the body that is in contact with the chair results in the greater comfort, but the human body often becomes uncomfortable, tired and fatigued if the same posture in the chair is maintained over a long period of time. It is now well established that to sustain long term comfort, a dynamic posture function is necessary; i.e., one which permits the chair member to be tilted or otherwise moved by the user relative to its support or base.
There are many types of chairs that provide a dynamic posture function, but virtually all such chairs encounter practical or economic problems. From the economic standpoint, enabling the chair member to move relative to its base necessarily involves some type of pivot mechanism that increases chair cost. This generally means that the dynamic posture function cannot be incorporated into lower cost chairs, such as stacking chairs sold to office product markets and audience seating markets.
Where mechanical movement has been included as a chair function, the mechanism generally is spring loaded and constantly seeks to return the chair to its upright position. This feature imposes added pressure on the body surface contact with the chair unless the chair can be locked in position. While a mechanical feature may be incorporated that enables the user to periodically move the chair into a desired tilt angle, this not only increases the cost of the chair but also requires periodic manual adjustment by the user.
We have found that this problem can be practically and economically solved with a tilt mechanism that permits an infinitely variable tilt over a predetermined range of movement as the result of normal body movement, and which remains in the position chosen by the user. The tilt mechanism has a built-in resistance which is frictional in the preferred embodiment, and operates on a substantially inertia free basis. The user may simply move his or her body forward or rearward, and the chair member follows in a smooth and flowing manner that is analogous to high viscosity fluid motion. When the desired position is reached, the user simply ceases his/her body movement, and the chair is thereafter retained in the desired position.
The tilt mechanism is relatively inexpensive, and both economically and efficiently provides a dynamic posture function to maintain substantially equal pressure distribution and body comfort over relatively long periods of time.
The broad invention of incorporating the unique tilt mechanism to accomplish the dynamic posture function finds application in a broad range of seating applications, and in particular in a sit/stand chair usable by persons who normally must remain on their feet during a particular job or task. An example is a grocery checkout clerk, who generally stands in a single, confined area. The grocery checkout task can be quite intense for the checkout clerk, involving long periods of standing (e.g., 4-8 hours) with relatively severe body strain.
An attempt has been made to solve the problem of discomfort by incorporating lean stands at the checkout counter, but such devices cannot provide a continuous body support function without the user experiencing discomfort. In particular, lean stands cannot distribute upper weight evenly over that part of the body that contacts the stand, resulting in point pressure that leads to discomfort. Further, a lean stand obviously cannot provide a dynamic posture function, requiring the clerk to move periodically to a more comfortable position.
The inventive chair which is disclosed solves these problems through the combination of a friction controlled tilt mechanism, a unique chair member and a selectively movable mobile base. The chair member has seat and back members that are relatively disposed at an open angle that is much larger than a conventional chair, and the seat member is uniquely configured for a straddle type support. With the chair in its forward tilt position, the user has substantial contact with both the seat and back members, but his/her feet may remain on the floor in a balanced position. As such, the chair is in essence leaned on by the user, but full body support is offered.
The user may also tilt the chair rearwardly over a range of positions through the use of the friction controlled mechanical pivot mechanism, and progressively greater support is transferred from the user's feet to the chair member. Whatever the desired tilt position, the unique chair provides support to the user's buttocks, thigh/pelvic area and lower back, and distributes weight in a manner which greater enhances the user's comfort.
The pivot mechanism uniquely incorporates friction disk brake elements formed from ultra high molecular weight polyethylene (UHMWP). Unlike most substances, UHMWP has static and dynamic coefficients of friction that are almost identical. The utilization of this material between interfacing elements of dissimilar materials (e.g., plated steel or anodized aluminum) results in a frictional interface that is substantially linear (similar to a hydraulic pump) as pressure is applied by the user to tilt the chair member. The chair member thus moves from one desired tilt position to another with little effort on the part of the user, and it is retained in any desired tilt position without any effort on the part of the user.
The chair member itself has been uniquely designed and sized to accommodate the vast majority of potential users. The publication Basic Design Measurements for Sitting by Clara A. Ritter, published by the University of Arkansas in 1959, includes seated body size contour data that facilitates the design of conventional chairs to accommodate body sizes from the 5th percentile female to the 95th percentile male. This data has been uniquely translated to the open angled sit/stand chair to likewise accommodate this broad percentile range.
The mobile base for the chair is designed to be maintained in an immobile position when it is in use, but it otherwise can be easily moved to a different floor location. In the preferred embodiment, this is accomplished through the use of a large pedestal base the diameter of which is sufficient to resist tipping throughout the range of tasks. The pedestal base is supported at three points by cylindrical rollers that are mounted in a fixed position and in relative opposition to one another. As such, the sit/stand chair will not easily roll to another position, although a simple lifting of the chair member at a single point will place primary support on a single roller, enabling the chair to be easily moved.
In an alternative embodiment, the chair base includes a relatively large circular housing and three spring loaded casters that are normally urged downward in contact with the floor or support surface. When the chair is not in use, the casters lift the chair and circular housing from the floor, and the chair can be easily moved. As soon as the user places any degree of weight on the chair the casters are automatically retracted, permitting the circular housing to contact the floor to prevent movement.